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Controlling spartina in the New River Estuary, Invercargill

Introduction

The eradication of spartina in the mud flats that make up the Invercargill estuary was thought to be an impossible task. Through dogged determination and hard work we are close to achieving this goal.

Spartina

Spartina flower, New River Estuary

Spartina, known as cordgrass, is native to Europe and was introduced to New Zealand as an estuarine stabiliser plant.

Two species of spartina were planted within the New River Estuary and there is now hybridisation between the two species:

Spartina townsendii which does not produce viable seeds, and

Spartina anglica which produces seed.

The estuary

The New River Estuary is a large tidal lagoon type estuary which drains eight catchments, including Oreti River, the third largest in Southland.

The planting of spartina has been detrimental to estuary health with:

a reduction in estuary fauna including mud snails, crabs and flatfish and a decline in wading bird species such as dotterels and spoonbills

an increase in sedimentation, causing the upper estuary to become shallow and the shell banks becoming stabilised.

The impact of spartina

Spartina was planted in the New River Estuary between 1930 and 1955 to reclaim what was perceived as waste land. Through planting and natural spread, spartina infested 800 ha of the estuary.

From here spartina spread to other harbours and estuaries within Southland: Jacobs River Estuary, Bluff Harbour, Haldane Estuary, Toetoes Harbour, Waikawa Harbour, Waumatuku Mouth, Mokomoko Inlet, Oreti River ,Waihopai Arm and Stewart Island. Many of these areas are now eradicated.

Spartina control

Early spartina control methods

Biodiversity ranger Graham Miller has led the control programme since it started. His innovative methods have been the key driver and success of this programme. These methods included: